Rotaviruses cause gastrointestinal disorders and diarrhea in a wide variety of avian and mammalian species, including man. Several serotypes of rotavirus have been identified, four of which (serotypes 1 to 4) are found in humans and five of which (serotypes 3 to 7) are found in other animals. Recent studies indicate that cross protection among strains belonging to different serotypes may occur in animals including man. Ijaz et al., J Virol (1990) (In Press); Flores et al., J Clin Microbiol (1989) 27:512-518. The rotavirus genome is thought to consist of eleven segments of double-stranded RNA. The eleven genes encode the production of at least six structural proteins of the virus. In complete virus particles, these six proteins occur in a double-shelled arrangement. The outer shell or capsid is comprised of three proteins--virus protein 7 (VP7), virus protein 4 (VP4), and a third protein which has not yet been well characterized. There are three inner shell proteins designated virus protein 1 (VP1), virus protein 2 (VP2), and virus protein 6 (VP6).
VP7 is the major outer shell glycoprotein with an approximate molecular mass of 38 kD in its unreduced form (as determined by SDS-PAGE) and 42 kD in its reduced form (as determined by SDS-PAGE). VP7 has approximately 325 amino acids. The amino acid sequence of several rotavirus isolates has been determined and the sequences are approximately 75 to 86% homologous. Regions of conservation among human and animal species have been reviewed by Estes, M. K. et al., Microbiol Rev (1989) 53:410-449. This protein is known to bind to host cells (Sabara, M. et al., J Virol (1985) 53:58-66). Epitope mapping of VP7 using neutralizing monoclonal antibodies has localized a neutralizing-absorption domain to a component peptide with an approximate molecular mass of 14 kD (Sabara, M. et al., supra). Synthetic peptides derived from within this 14 kD fragment have also been shown to neutralize viral infectivity (Ijaz et al., supra).
A second outer capsid protein, VP4 (formerly designated VP3), is composed of 776 amino acids and has an approximate molecular mass of 82 kD in its unreduced form and 84 kD in its reduced form. The sequence of bovine VP4 has been determined (Potter, A. A. et al., Nucl Acid Res (1987) 15:4361) as has the partial amino acid sequence for simian VP4 (Mackow, et al., Proc Natl Acad Sci USA (1988) 85:645-649. VP4 possesses hemagglutinating activity, and induces the production of neutralizing antibodies which provide heterotypic passive protection in vivo (Offit, P. A. et al., J Virol (1986) 58:700-703). VP4 is responsible, in combination with VP7, in determining virus serotype.
Dimers of VP4 combine to form the surface spikes of rotavirus that extend distally from the rotavirus outer shell. VP4 is important in the penetration of the virus into the host cell and infectivity is increased by the cleavage of VP4 by trypsin. Trypsin enhanced infectivity is a common feature of all rotaviruses and the cleavage site for trypsin is also conserved as reviewed in Estes et al. (supra).
The inner capsid of rotavirus includes at least three proteins designated VP1, VP2 and VP6. Of interest herein is VP6 which is a 45 kD protein. Bovine VP6 appears to exist in trimeric units in both the virus particle and in infected cells, with the intersubunit linkage consisting of noncovalent interactions. These trimeric units complex further by virtue of disulfide bridges into larger units which likely represent the ring-like structures observed by several investigators using electron microscopy.
VP6 has been identified as the subgroup antigen and has also been described as the common rotavirus group antigen since some monoclonal antibodies raised against this protein react with all rotaviruses and polyclonal serum raised against a single rotavirus type can detect most other rotavirus strains. In addition to its antigenic properties, this nucleocapsid protein is extremely immunogenic and several investigators have found that the antibody raised to this protein has neutralizing ability. (See, e.g. Offit, et al., J Virol (1986) 58:700-703).
VP6 is an effective carrier protein (Redmond, M. J., et al. Mol Immunol (1990) (In Press) and VP4 is able to associate with VP6 monomeric and oligomeric protein units. (Redmond, M. J., et al. supra). The VP4-VP6 association has been shown to withstand harsh treatment such as boiling in SDS. Additionally, VP6 is capable of forming particles in vitro with VP2 and VP7 using a calcium dependent process (Ready, K. F. M., et al., Virology (1988) 167:269-273). The resulting assembly is immunoreactive with antibodies specific for the whole virus as well as for immunodominant sites on VP6 and VP7 and this immunoreactivity is equivalent to that of native bovine rotavirus (BRV). (Ready, K. F. M., et al., supra).
The present invention provides assembled viral particles including peptides or proteins corresponding to VP7 and/or VP4, or immunogenic regions thereof, in combination with VP6. These assembled particles are effective as vaccines and in eliciting the production of neutralizing antibodies. Such a vaccine provides an alternative to the use of a live attenuated virus vaccine.